Radiation’s Double-Edged Sword

Image courtesy of IAEA

—from the International Stroke Conference in San Antonio 

Ionizing radiation—useful for imaging and therapy—has undoubtedly been a boon to medicine.  The ability to quickly and noninvasively peek inside the body has not only led to faster diagnoses, but more accurate ones.  The ability to target cancerous tissue with a beam of radiation has improved therapeutic options for many cancer patients. 

However, it comes with a cost.  In the past few months, newspaper headlines have detailed cases of accidental exposure of patients to dangerously high doses of ionizing radiation for both imaging and radiotherapy.  The cases were alarming enough that members of the  House Energy and Commerce Committee’s Subcommittee on Health called radiology organizations, manufacturers, and experts to testify on ways to improve the safety of medical technology involving ionizing radiation to prevent accidents like those in the headlines. 

As that hearing occurred in Washington, data presented at the ISC was a stark reminder that even if  procedures using ionizing radiation meet safety requirements, patients could be exposed to concerning levels of ionizing radiation over the course of diagnosis and treatment of just one condition.  At the ISC,  Dr. Venkatesh Aiyagari, a professor of neurology at the University of Illinois, presented data on cumulative radiation exposure for patients with subarachnoid hemorrhage (SAH) over the course of their hospital stay. 

In the retrospective study 107 patients with SAH underwent 1,458 CT scans.  The researchers looked at cumulative effective dose, a term which refers to the radiation risk averaged over the entire body.  Over the course of treatment, 24% received moderate effective doses (>3-20 mSv), 39% received high effective doses (>20-50 mSv), and 35% recieved very high effective doses (>50 mSv). 

Let’s put that into perspective.  The U.S. Nuclear Regulatory Commission estimates the average annual radiation exposure from natural sources to an individual in the United States is about 3 millisieverts.  The NRC requires that its licensees limit maximum radiation exposure to individual members of the public to 1mSv per year and limit occupational radiation exposure to adults working with radioactive material to 50 mSv per year. 

Of course, Dr. Aiyagari’s study looked only at effective doses for one condition.  The effects of ionizing radiation are cumulative, so all of those dental x-rays, chest x-rays, and CT scans add up.  Right now, no one is tasked with keeping track, though that may change.  Earlier this year the NIH’s Clinical Center announced that radiation exposure for procedures at the center would be documented in the patient’s EHR.   Around the same time, FDA announced an initiative to reduce unnecessary radiation exposure from CT, nuclear medicine studies, and fluoroscopy.  Possible steps may include requiring manufacturers to display, record, and report equipment settings and radiation dose. 

It seems clear that physicians can expect changes in the way that medical radiation is tracked and some rethinking about how necessary some scans are. 

—Kerri Wachter ( @knwachter on Twitter)